Field of the Invention
The present invention relates to an image forming apparatus.
Description of the Related Art
In image forming apparatuses such as printers which use an electrophotographic image forming system (electrophotographic process), image recording is performed in the following manner: an electrophotographic photosensitive member (hereinafter referred to as a “photosensitive member”) serving as an image bearing member is uniformly charged; the charged photosensitive member is selectively exposed to form an electrostatic image on the photosensitive member; the electrostatic image formed on the photosensitive member is visualized as a toner image using toner in developer; then, the toner image formed on the photosensitive member is transferred to a recording material such as a recording sheet or a plastic sheet; and the toner image transferred to the recording material is further heated and pressurized so as to be fixed onto the recording material.
Such an image forming apparatus generally needs refilling of developer and maintenance of various process means. To facilitate the developer refilling operation and the maintenance of the various process means, a technique has been put to practical use in which the photosensitive member, charging member, developing means, cleaning means, and the like are collectively stored in a frame member to form a process cartridge that can be installed in and removed from the image forming apparatus. The process cartridge system enables the provision of an image forming apparatus with high usability.
In conventional developing apparatuses used for image forming apparatuses, a method of applying a coating agent (lubricant) to a developing roller (developer bearing member) in order to suppress turn-up of a regulating blade (developer regulating member) and to reduce a driving torque has been widely used. In Japanese Patent Application Laid-open No. H2-298971, powder with the same polarity as that of toner is used as a coating agent for the developing roller. Japanese Patent Application Laid-open No. H8-227212 proposes that, as a coating agent, the following be coated at least on a surface of the toner supply roller (developer supply member): powder with no charging capability or powder that is charged with the same polarity as the developer and that has a charging capability having an absolute value equivalent to or smaller than the charging capability of the developer. On the other hand, a technique for conventional image forming apparatuses is widely known in which the developer is periodically discharged so as to be restrained from being degraded. Japanese Patent Application Laid-open No. 2006-23327 indicates that, in order to suppress degradation of the toner in the developer, an operation of periodically discharging the developer is performed such that toner consumption for each page is constant.
The situation described below may occur when a coating agent is used in the manner of Japanese Patent Application Laid-open No. H2-298971 and Japanese Patent Application Laid-open No. H8-227212. During the latter half of life of the image forming apparatus, durability of the developer or durability of a developing roller or a developing blade is degraded to deteriorate charging characteristics of the toner. Then, an initial coating agent remaining in a developing chamber may move to the recording material along with a toner image at the time of image formation. The coating agent attached to the recording material may appear as streaks on the image or streak-like fogging images on a blank portion of the paper. Thus, the coating agent initially applied to the developing roller is desirably discharged to the outside of the developing chamber quickly.
However, for such a discharging method and a discharge frequency according to the related art as described in Japanese Patent Application Laid-open No. 2006-23327, the coating agent may fail to be fully discharged and remain in the developing chamber. When image formation is performed with the coating agent remaining in the developing chamber, the durability of the developer may be deteriorated or the developing roller may be degraded to deteriorate the charging characteristics of the toner, causing the coating agent to move to the recording material along with the toner image. This may also result in abnormal images such as streaks and fogged images.